Cleaning means for an overcoated photoconductive surface

ABSTRACT

An electrophotographic apparatus and process incorporating an overcoated photoconductor element, an erasing light being utilized after transfer of the toned image to copy paper. The erasing light is used for improvement of image quality by the elimination of image ghosting and edging effect.

United States Patent [19] Estandarte June 25, 1974 CLEANING MEANS FOR ANOVERCOATED PHOTOCONDUCTIVE SURFACE [75] Inventor: Adolfo UmadhayEstandarte,

Sunnyvale, Calif.

[73] Assignee: SCM Corporation, New York, NY.

[22] Filed: July 13, 1972 [21] Appl. No.: 271,504

[52] U.S. Cl 355/15, l5/l.5,96/1.4 [51] Int. Cl. G03b 15/00 [58] Fieldof Search 355/15; 96/l.4; l5/1.5

[56] References Cited UNITED STATES PATENTS 3,355,289 ll/l967 Hall etal. 96/l.4 3,438,706 4/1969 Tanaka et al.. 96/l.4 3,637,306 l/l972Cooper 355/15 OTHER PUBLICATIONS Nonoptical Electrostatic Reproduction"by Y.

Moradzadeh et 21]., IBM Technical Bull., Vol. 8, No. 4, September, 1965,pg. 491-492.

Reduction of Toner-Filming in Electrophotography" by N. Crooks et al.,IBM Technical Bull., Vol. 12, No. 12, May, 1970, pg. 2,094.

Removal of Electrostatic Images by Coronas by T. F. Ceicel, IBM Tech.Bull. Vol. 12, No. 12, May 1970, pg. 2,116.

Discharge of Unwanted Potentials on Photoconductive Insulating Platesand Dielectric Surfaces by F. A. Hawn, IBM Tech. Bull., Vol. 12, No. 12,May, 1970, pg. 2,277.

Primary Examiner-Richard L. Moses Attorney, Agent, or FirmArmand G.Guibert; Milton M. Wolson [57] ABSTRACT An electrophotographic apparatusand process incorporating an overcoated photoconductor element, anerasing light being utilized after transfer of the toned imag to copypaper. The ei'asing light ieiisedTdfifii provement of image quality bythe elimination of image ghosting and edging effect.

3 Claims, 2 Drawing Figures CLEANING MEANS FOR AN OVERCOATEDPHOTOCONDUCTIVE SURFACE BACKGROUND OF THE INVENTION tems using eitherdry or wet development techniques ing techniques as discussed on pages274-279 of Xe- 2 rography and Related Processes, edited by John H.Desauer and Harold E. Clark, The Focal Press, London and New York, 1965,but these have certain disadvantages such as reduction of exposurelatitude. The solution to the image ghosting problem has beentraditionally attempted by use of a discharge lamp and rotating brushesfor cleaning the toned image from the drum as described on pages 470,503 of the above-mentioned publication. Though illumination completelydissipates charges on selenium photoconductors, it does not have thiseffect with overcoated photoconductors, as is known (page 458 of theabove-mentioned publication). A discharging or erasing corona alone hasbeen used to solve image ghosting problems with overcoatedphotoconductor elements as disclosed in the Japanese Patent Gazette,Nov. 17, 1967, Patent Publication No. 23910/1967, entitledElectrophotographic Process and invented by Tanaka et al., but thisalone has not been completely satisfactory.

Accordingly, there is a need in the art for a simple apparatus andmethod of eliminating both image ghosting and edging effect onelectrographic copies made with systems based on overcoatedphotoconductor elements, and thus to improve the image quality therein.

BRIEF SUMMARY OF THE INVENTION An object of the invention is a simplemethod and apparatus of the overcoated photoconductor type for producingelectrographic copies in which both image ghosting and edging effectsare eliminated, thus producing images of greatly improved quality.

A further object is to provide an improved method of cleaning thesurface of an overcoated photoconductor element.

The invention concept resides in an electrophotographic apparatus havingan overcoated photoconductor element; means depositing a layer ofcharged particles on a surface of the photoconductor element; means forexposing the charged surface to a light image; means for toning theexposed surface; a copy sheet; means bringing the copy sheet intomomentary contact with the toned surface; and means transferring theimage from the toned surface to the copy sheet, in combination with alight source illuminating the toned surface subsequent to transfer ofthe image.

BRIEF DESCRIPTION OF THE DRAWING The invention will be described withreference to the drawing, in which:

FIG. la shows the apparatus according to the invention includingproduction of a latent image on an overcoated photoconductor element,toning of the latent image, transfer of the toned image to a suitablecopy paper, and finally the neutralization of the electrostatic chargesof the latent image by means including an erasing light; and

FIG. 1b shows a cross section of a photoconductor element of FIG. la.

DESCRIPTION OF THE PREFERRED EMBODIMENT The electrophotographic processpresented herein can be used with either dry toner or wet toner. Forpurposes of illustration, I will show only how the dry toning techniquewill apply to this invention. FIG. la shows an electrophotographicapparatus using an appropriate dry toning technique to produce an imageon a copy sheet 16 fed along a drum 2. The electrophotographic processdeposits a latent image 9 on an overcoated photoconductor element 3formed on the surface of drum 2. Photoconductor element 3 used in thisinvention (better shown in FIG. lb) is comprised of a conducting support3c, a photoconductor layer 3b, and an insulating layeror overcoat 3a.Such elements are known in the art (US. Pat. No. 3,457,070, forinstance). Prior to formation of latent image 9, element 3 is given auniform surface charge by subjecting it to a discharge from a coronasource 4 (well known in the art), element 3 being maintained in thedark. Although not critical at this point, element 3 must be illuminatedonly when so indicated in the description, as will beevident. Asubsequent charging and exposing sequence, described below in detail,results in formation of latent image 9 actually an electrostatic chargepattern 9b on outer surface 3d of photoconductor element 3 (see FIG.lb). Latent image 9 is later developed by applying an appropriate tonermaterial to charged surface 3d and the toned image 9a then transferredto a sheet of copy paper 16, which may be plain or bond paper. Theresidual pattern remaining on surface 3d is then removed by action of anerasing corona 13, a mechanical brush l5 and, according to theinvention, an erasing light 14, as will be described.

Referring still to FIG. la, corona charging source 4 is employed toapply a uniform precharge in the positive or in the negative to surface3d of photoconductor element 3. For purposes of this description,however, corona charge unit 4 will be assumed to apply positive charges.Photoconductor element 3, shown in FIG. 1b, may be comprised, forexample, of a top insulator 3a made of Mylar (T.M.), which also acts asa protective coating, a photoconductor material 3b made of cadmiumsulfide held in a binder such as cellulose acetate, and a conductivebacking 3c such as metal foil for allowing uniform distribution ofcharges. Other structures for photoconductor element 3 may be found inpreviously-mentioned US. Pat. No. 3,457,070.

Next, an original pattern 7a is projected through lens 8 and atransparent imaging corona source 5. Simultaneously, a negative coronadischarge from corona source 5 (polarity opposite to that of corona unit4) is applied on the surface 3d of precharged insulating layer 3a. Apreliminary, medium contrast latent image 9 of original pattern 7a isthen obtained by virtue of changes in the surface potentials inaccordance with the light and dark areas of original pattern 7a, theamount of discharge being controlled by the time and intensity of thedischarge from corona source 5 alone in the light areas. In the darkareas, these factors together with the strength of the trapped negativecharge in the photoconductor layer 3b at or near its border withinsulating layer 3a determine the amount of decrease in the precharge.The discharge in the dark areas is thus less than in light areas becausethe photoconductor layer 3b under the latter areas becomes conductiveand allows the previously trapped negative charges to flow out toconductive backing 3c. Contrastingly, layer 3b under the dark areasremains nonconductive and the trapped negative charges cannot flow out,preventing much dissipation of the positive precharge in dark areas ofsurface 3d. Note further, that after exposure to pattern 7a, trappednegative charges in the dark areas significantly reduce the surfacepotential in such areas because of contribution by these charges to theexternal field.

Then, surface 3d of insulating layer 3a is uniformly illuminated bylightsource 10, and thereby a reversed, high contrast latent image 9b of theoriginal pattern 7a is formed on surface 3d of insulating layer 3a. Thereason for the reversal and charge pattern intensification (contrastamplification), as theorized in the previously-referenced JapaneseGazette Publication, is that further exposure to light does not resultin a great change in surface potential in the areas of surface 3d whichwere previously exposed to light from pattern 7a, but the same is nottrue for those areas which were then dark. In this latter case, thepreviously trapped negative charges flow out to the conductive backing3c since photoconductor layer 3b now shows a low resistivity because ofillumination by post-flooding light source 10. The related positivecharges on outer surface 3d, unaffected by the light, will hold only afew of the negative charges near the border with insulating layer 3a andthe field exerted by the outer surface charges will be predominant suchthat the surface potential of the dark areas increases markedly and to avalue considerably greater than that of the light areas.

Latent image 9b is then developed in station 11 by known techniques suchas either aerosol or magnetic brush toning. The developer is mainlycomposed of charged colored particles, as is known, attracted towardsthe latent image to form a visible image 9a.

The developed image 90 is next brought into contact with sheet 16 forpurposes of transferring the image. In this respect, note that lightsource 6 is timed to come on in relation to the feeding of copy sheet 16such that once a toned or developed image 9a has been obtained, it willmake contact with paper 16 in time to locate the image on paper 16 inproper reference to leading edge 160. Similarly, light 6 must go offwhen the trailing edge 16d of paper 16 passes a certain point. Thoughnot shown, such photographic projection control techniques are wellknown in the art, examples being found in US. Pat. Nos. 3,343,450 and3,345,925. Sheet 16 is fed on a platfonn 25 which guides paper 16 to apickup roller 17, driving sheet 16 such that it makes contact with andis attracted to charged photoconductor element 3 on drum 2. As sheet 16moves along in contact with drum 2, the developed image 9a istransferred to sheet 16 by means of a transfer corona source 1 1 whichsprays positive charges (opposite in polarity to that of toner particles26 onto the back 16a of sheet 16 thus pulling toner particles 26 fromphotoconductor surface 3d towards surface 16b of transfer sheet 16.After the toner transfer, sheet 16 is separated from drum 2 by, say, anair blade 21 and then leading edge is caught by a vacuum conveyor 24,thus moving sheet 16 towards a fusing station 22 upon clockwise rotationof drive rollers 20,23. Since dry toner has been utilized in theembodiment described, fusing of the image can be done simply by aninfrared light source or other known fixing device. Once the image isfused, sheet 16 is sent out of the machine via an exit platfonn 24a.

As drum 2 continues its counterclockwise rotation, the residual image 9con photoconductor element 3 passes a station containing a DC or an ACerasing corona 13, which will actively neutralize the residual chargepattern of image 9c on surface 3d by spraying a negative charge towardthat surface. If any part of the system is at less than optimumefficiency, however, uniformity of large image areas (dark areas) andcleanliness of background areas (light areas) on paper 16 will remainsignificantly good because of the presence of an erasing light 14, whichuniformly illuminates the entire area of photoconductor element 3previously exposed to corona source 13. This illumination by an erasinglight 14 effectively places the entire area at a neutral energy state byallowing trapped charges in the border area between photoconductor layer3b and insulating layer 3a to flow out to conductive backing layer 3c.The effect of the negative charge from erasing corona 13 as modified byillumination from erasing light 14 is that any residual electrostaticcharge pattern on photoconductor element 3 will be neutralized. Thiseliminates image ghosting and edging effect and improves image quality.

To insure that dark toner particles will not build up undesirably onphotoconductor element 3, it is passed through a cleaning stationcontaining a brush 15 having a counter-rotating motion along the surfaceof drum 2. In the electrophotographic process using a dry toningtechnique, the material of brush 15 could be of a soft animal furmaterial.

In summary, I have described herein an electrophotographic apparatus andmethod with which images of improved quality are achieved withphotoconductor elements of the overcoated type. In this apparatus, anappropriate dry toner is applied to an image generated on an overcoatedphotoconductor element 3 formed on a drum 2, and transfer of toned image9a to either a plain or bond paper sheet 16 is accomplished by atransfer corona 12. After image transfer is completed, the residualimage on photoconductor element 3 is then neutralized or effectivelyeliminated by use of an erasing light 14 with improvement in imagequality by cleanliness of the background area and uniformity of shadetone in large image-fill areas.

While a particular embodiment of the invention has been shown anddescribed, modifications such as omission of post-flooding light 10 orerasing corona 13 or cleaning brush [5 are envisioned, and it isintended in the claims to cover all such modifications which fall withinthe spirit and scope of the invention.

What is claimed is:

1. An electrophotographic apparatus having an overcoated photoconductorelement; means depositing a layer of charges on a surface of thephotoconductor element, said deposited charges having a first polarity;means exposing said charged surface to a light image comprising atransparent corona source spraying on said charged surface charges of apolarity opposite to said deposited charges and means for projecting alight image through said transparent corona source simultaneously withsaid spraying of oppositely polarized charges thereby producing apreliminary latent image, and a light source for uniformly illuminatingsaid medium contrast latent image to thereby obtain a final, highercontrast latent image; means applying a toner to said exposed surface; acopy sheet; means for bringing said copy sheet into momentary contactwith the toned surface; and means transferring the image from said tonedsurface to said copy sheet; in combination with a further light sourceilluminating the toned surface subsequent to transfer of the image andan erasing corona source spraying charges of a polarity opposite to saiddeposited charges on said toned surface subsequent to transfer of saidimage.

2. Apparatus as defined in claim 1, wherein said toned surface is on theperiphery of a drum having a particular direction of rotation and saidsource of erasing corona appears prior to said further light source insaid direction of rotation.

3. Apparatus as defined in claim 2, further including means contactingsaid toned surface and operating to remove physically the residue ofsaid toner subsequent to said transfer, said residue removing meansappearing after said further light source in said direction of rota-UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,819,262 Dated June 25, 1974 lnventor(s) Adolfo Umadhay Estandarte Itis. certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 4, line 60, after "of", delete "post-flooding light 10 or erasingcorona 13 or" Column 6, line 4, after "image", 7 insert and, prior toillumination by' said furtherlight source Delete lines 5-9 (Claim 2)line i0, change "3" to 2 and "2" to 1 Signed and sea-led this 7th day ofJanuary 1975.

(SEAL) Attest: I v c McCOY M. GIBSON JR. c. MARSHALLDANN AttestingOfficer I Commissioner of Patents FORM PO-105O (10-69) I uscoMM-ocGUSTO-P69 R U.$. GOVERNMENT PRINTING OFFICE I!" 0-80-33,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,819,262 Dated June 25, 1974 Inventofls) Adolfo Umadhay Estandarte Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 4, line 60, after "of", delete "post-flooding light 10 or erasingcorona 13 or" Column 6, line 4, efter "image", insert and prior toillumination byflsaid fur'thenlight source Delete lines 5-9 (Claim 2)line 10, change "3" to 2 and "2" to 1 Signed and sealed this 7th day ofJanuary 1975.

(SEAL) Attest; v

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer 7 Commissioner ofPatents IFORM PO-105O (10-69) uscoMM-Dc sows-Pu, i ".5. GOVERNMENTPRINTING OFFICE I!" 0-!484

1. An electrophotographic apparatus having an overcoated photoconductorelement; means depositing a layer of charges on a surface of thephotoconductor element, said deposited charges having a first polarity;means exposing said charged surface to a light image comprising atransparent corona source spraying on said charged surface charges of apolarity opposite to said deposited charges and means for projecting alight image through said transparent corona source simultaneously withsaid spraying of oppositely polarized charges thereby producing apreliminary latent image, and a light source for uniformly illuminatingsaid medium contrast latent image to thereby obtain a final, highercontrast latent image; means applYing a toner to said exposed surface; acopy sheet; means for bringing said copy sheet into momentary contactwith the toned surface; and means transferring the image from said tonedsurface to said copy sheet; in combination with a further light sourceilluminating the toned surface subsequent to transfer of the image andan erasing corona source spraying charges of a polarity opposite to saiddeposited charges on said toned surface subsequent to transfer of saidimage.
 2. Apparatus as defined in claim 1, wherein said toned surface ison the periphery of a drum having a particular direction of rotation andsaid source of erasing corona appears prior to said further light sourcein said direction of rotation.
 3. Apparatus as defined in claim 2,further including means contacting said toned surface and operating toremove physically the residue of said toner subsequent to said transfer,said residue removing means appearing after said further light source insaid direction of rotation.